The Encyclopedia Americana (1920)/Rat
RAT, any of several large rodents of the mouse family (see Mouse), especially two species of “house-rats” now habituated to civilization in all parts of the world. The black rat (Musrattus) is of light and slender build, about seven inches in length, usually of a bluish black color, but sometimes grayish, and has quite large, thin ears. The brown rat (M. decumanus) or Norway rat, as it is often inappropriately styled, is much heavier and larger, with short, rounded ears and a dull brown color. Both species are believed to be natives of China but the black rat was abundant in Europe at least as early as the 13th century. The brown rat migrated from western China, entering Russia in great numbers in 1727, and from there quickly spreading over Europe, which was fully occupied by it by the middle of the 18th century. By its greater fecundity and ferocity it quickly overcame the black rat, which it has now replaced in most parts. It infested ships and by this means has been carried to all parts of the world. Its wonderful capacity for increase (from 20 to 50 annually), its boldness, tough, elastic constitution and adaptable nature, make it everywhere dominant, and its omnivorous habits, voracity and destructiveness frequently lead it to become a source of great annoyance, loss and disease about human habitations. The ferocity of this species when brought to bay is well known; and when driven by hunger it is so ravenous that neglected babies have been known to be killed and eaten by them, and a few cases are recorded where even able-bodied men have suffered a like fate when attacked by hordes of rats. They are also agents in the spread of disease, particularly bubonic plague and trichinoses. Against their many faults may be set the solitary virtue that they serve a useful purpose as scavengers in the city sewers, etc. The albino and black and white pied rats sold for pets by bird dealers are derived from the black rat, which has a far milder disposition. The rats of the United States include the black and brown of Norway, above described; the roof, or white-bellied (M. tectorum) of the southern States, named from its preference for thatched roofs for its abode; the Florida (neotorua Floridana) a habitat of the Gulf States, common to wild places and swamps, and frequently nesting in trees; the Cotton (Sigmodon hispidus), named from its use of cotton in forming its nest; and the Rocky Mountain, which is destructive to the trappings and stores of campers. Rat skins make fine leather for gloves.